Dimmer switch for use with lighting circuits having three-way switches

ABSTRACT

A smart dimmer switch for control of a lighting load from an AC voltage source can replace any switch in a three-way or four-way lighting control system. The smart dimmer switch can be connected on the line-side or the load-side of a three-way system with a standard three-way switch in the other location. Further, the dimmer switch can replace a four-way switch in a four-way system and is operable to be coupled to two standard three-way switches. The dimmer switch includes either one or two semiconductor switches to control the intensity of the connected lighting load. The dimmer switch preferably includes a sensing circuit for detecting an electrical characteristic (i.e., either a voltage or a current) at a terminal of the dimmer to determine the state of the connected three-way switch(s) or four-way switch. The dimmer switch preferably controls the state of the semiconductor switch in response to either a toggle of any of the other switches in the system or an actuation of a toggle button of the dimmer switch.

RELATED APPLICATIONS

This application is a continuation-in-part of commonly-assigned U.S.patent application Ser. No. 11/447,496, filed Jun. 6, 2006, entitledDIMMER SWITCH FOR USE WITH LIGHTING CIRCUITS HAVING THREE-WAY SWITCHES,which claims priority from commonly-assigned U.S. ProvisionalApplication Ser. No. 60/687,690, filed Jun. 6, 2005, entitledINTELLIGENT THREE-WAY AND FOUR-WAY DIMMERS. The entire disclosures ofboth applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to dimmer switches for electrical wiringsystems having three-way switches. In particular, the present inventionrelates to a dimmer switch that can be substituted for a four-wayswitch, a line-side three-way switch, or a load-side three-way switch inlighting circuits having either two or more points of control, such as,for example, a four-way system.

2. Description of the Related Art

Three-way and four-way switch systems for use in controlling loads inbuildings, such as lighting loads, are known in the art. Typically, theswitches used in these systems are wired to the building'salternating-current (AC) wiring system, are subjected to AC sourcevoltage, and carry full load current, as opposed to low-voltage switchsystems that operate at low voltage and low current, and communicatedigital commands (usually low-voltage logic levels) to a remotecontroller that controls the level of AC power delivered to the load inresponse to the commands. Thus, as used herein, the terms “three-wayswitch”, “three-way system”, “four-way switch”, and “four-way system”mean such switches and systems that are subjected to the AC sourcevoltage and carry the full load current.

A three-way switch derives its name from the fact that it has threeterminals and is more commonly known as a single-pole double-throw(SPDT) switch, but will be referred to herein as a “three-way switch”.Note that in some countries a three-way switch as described above isknown as a “two-way switch”.

A four-way switch is a double-pole double-throw (DPDT) switch that iswired internally for polarity-reversal applications. A four-way switchis commonly called an intermediate switch, but will be referred toherein as a “four-way switch”.

In a typical, prior art three-way switch system, two three-way switchescontrol a single load, and each switch is fully operable toindependently control the load, irrespective of the status of the otherswitch. In such a system, one three-way switch must be wired at the ACsource side of the system (sometimes called “line side”), and the otherthree-way switch must be wired at the load side of the system.

FIG. 1A shows a standard three-way switch system 100, which includes twothree-way switches 102, 104. The switches 102, 104 are connected betweenan AC voltage source 106 and a lighting load 108. The three-way switches102, 104 each include “movable” (or common) contacts, which areelectrically connected to the AC voltage source 106 and the lightingload 108, respectively. The three-way switches 102, 104 also eachinclude two fixed contacts. When the movable contacts are making contactwith the upper fixed contacts, the three-way switches 102, 104 are inposition A in FIG. 1A. When the movable contacts are making contact withthe lower fixed contact, the three-way switches 102, 104 are in positionB. When the three-way switches 102, 104 are both in position A (or bothin position B), the circuit of system 100 is complete and the lightingload 108 is energized. When switch 102 is in position A and switch 104is in position B (or vice versa), the circuit is not complete and thelighting load 108 is not energized.

Three-way dimmer switches that replace three-way switches are known inthe art. An example of a three-way dimmer switch system 150, includingone prior art three-way dimmer switch 152 and one three-way switch 104is shown in FIG. 1B. The three-way dimmer switch 152 includes a dimmercircuit 152A and a three-way switch 152B. A typical, AC phase-controldimmer circuit 152A regulates the amount of energy supplied to thelighting load 108 by conducting for some portion of each half-cycle ofthe AC waveform, and not conducting for the remainder of the half-cycle.Because the dimmer circuit 152A is in series with the lighting load 108,the longer the dimmer circuit conducts, the more energy will bedelivered to the lighting load 108. Where the lighting load 108 is alamp, the more energy that is delivered to the lighting load 108, thegreater the light intensity level of the lamp. In a typical dimmingoperation, a user may adjust a control to set the light intensity levelof the lamp to a desired light intensity level. The portion of eachhalf-cycle for which the dimmer conducts is based on the selected lightintensity level. The user is able to dim and toggle the lighting load108 from the three-way dimmer switch 152 and is only able to toggle thelighting load from the three-way switch 104. Since two dimmer circuitscannot be wired in series, the three-way dimmer switch system 150 canonly include one three-way dimmer switch 152, which can be located oneither the line side or the load side of the system.

A four-way switch system is required when there are more than two switchlocations from which to control the load. For example, a four-way systemrequires two three-way switches and one four-way switch, wired in wellknown fashion, so as to render each switch fully operable toindependently control the load irrespective of the status of any otherswitches in the system. In the four-way system, the four-way switch isrequired to be wired between the two three-way switches in order for allswitches to operate independently, i.e., one three-way switch must bewired at the AC source side of the system, the other three-way switchmust be wired at the load side of the system, and the four-way switchmust be electrically situated between the two three-way switches.

FIG. 1C shows a prior art four-way switching system 180. The system 180includes two three-way switches 102, 104 and a four-way switch 185. Thefour-way switch 185 has two states. In the first state, node A1 isconnected to node A2 and node B1 is connected to node B2. When thefour-way switch 185 is toggled, the switch changes to the second statein which the paths are now crossed (i.e., node A1 is connected to nodeB2 and node B1 is connected to node A2). Note that a four-way switch canfunction as a three-way switch if one terminal is simply not connected.

FIG. 1D shows another prior art switching system 190 containing aplurality of four-way switches 185. As shown, any number of four-wayswitches can be included between the three-way switches 102, 104 toenable multiple location control of the lighting load 108.

Multiple location dimming systems employing a smart dimmer switch and aspecially designed remote (or “accessory”) switch that permit thedimming level to be adjusted from multiple locations have beendeveloped. A smart dimmer is one that includes a microcontroller orother processing means for providing an advanced set of control featuresand feedback options to the end user. For example, the advanced featuresof a smart dimmer may include a protected or locked lighting preset,fading, and double-tap to full intensity. To power the microcontroller,smart dimmers include power supplies, which draw a small amount ofcurrent through the lighting load each half-cycle when the semiconductorswitch is non-conducting. The power supply typically uses this smallamount of current to charge a storage capacitor and develop adirect-current (DC) voltage to power the microcontroller. An example ofa multiple location lighting control system, including a wall-mountablesmart dimmer switch and wall-mountable remote switches for wiring at alllocations of a multiple location dimming system, is disclosed incommonly assigned U.S. Pat. No. 5,248,919, issued on Sep. 28, 1993,entitled LIGHTING CONTROL DEVICE, which is herein incorporated byreference in its entirety.

Referring again to the system 150 of FIG. 1B, since no load currentflows through the dimmer circuit 152A of the three-way dimmer switch 152when the circuit between the supply 106 and the lighting load 108 isbroken by either three-way switch 152B or 104, the dimmer switch 152 isnot able to include a power supply and a microcontroller. Thus, thedimmer switch 152 is not able to provide the advanced set of features ofa smart dimmer to the end user.

FIG. 2 shows an example multiple location lighting control system 200including one wall-mountable smart dimmer switch 202 and onewall-mountable remote switch 204. The dimmer switch 202 has a Hot (H)terminal for receipt of an AC source voltage provided by an AC powersupply 206, and a Dimmed Hot (DH) terminal for providing a dimmed-hot(or phase-controlled) voltage to a lighting load 208. The remote switch204 is connected in series with the DH terminal of the dimmer switch 202and the lighting load 208, and passes the dimmed-hot voltage through tothe lighting load 208.

The dimmer switch 202 and the remote switch 204 both have actuators toallow for raising, lowering, and toggling on/off the light intensitylevel of the lighting load 208. The dimmer switch 202 is responsive toactuation of any of these actuators to alter the dimming level (or powerthe lighting load 208 on/off) accordingly. In particular, actuation ofan actuator at the remote switch 204 causes an AC control signal, orpartially rectified AC control signal, to be communicated from thatremote switch 204 to the dimmer switch 202 over the wiring between theAccessory Dimmer (AD) terminal of the remote switch 204 and the ADterminal of the dimmer switch 202. The dimmer switch 202 is responsiveto receipt of the control signal to alter the dimming level or togglethe load 208 on/off. Thus, the load can be fully controlled from theremote switch 204.

The user interface of the dimmer switch 202 of the multiple locationlighting control system 200 is shown in FIG. 3. As shown, the dimmerswitch 202 may include a faceplate 310, a bezel 312, an intensityselection actuator 314 for selecting a desired level of light intensityof a lighting load 208 controlled by the dimmer switch 202, and acontrol switch actuator 316. The faceplate 310 need not be limited toany specific form, and is preferably of a type adapted to be mounted toa conventional wall-box commonly used in the installation of lightingcontrol devices. Likewise, the bezel 312 and the actuators 314, 316 arenot limited to any specific form, and may be of any suitable design thatpermits manual actuation by a user.

An actuation of the upper portion 314A of the actuator 314 increases orraises the light intensity of the lighting load 208, while an actuationof the lower portion 314B of the actuator 314 decreases or lowers thelight intensity. The actuator 314 may control a rocker switch, twoseparate push switches, or the like. The actuator 316 may control a pushswitch, though the actuator 316 may be a touch-sensitive membrane. Theactuators 314, 316 may be linked to the corresponding switches in anyconvenient manner. The switches controlled by actuators 314, 316 may bedirectly wired into the control circuitry to be described below, or maybe linked by an extended wired link, infrared (IR) link, radio frequency(RF) link, power line carrier (PLC) link, or otherwise to the controlcircuitry.

The dimmer switch 202 may also include an intensity level indicator inthe form of a plurality of light sources 318, such as light-emittingdiodes (LEDs). Light sources 318 may be arranged in an array (such as alinear array as shown) representative of a range of light intensitylevels of the lighting load 208 being controlled. The intensity levelsof the lighting load 208 may range from a minimum intensity level, whichis preferably the lowest visible intensity, but which may be “full off”,or zero, to a maximum intensity level, which is typically “full on”, orsubstantially 100%. Light intensity level is typically expressed as apercent of full intensity. Thus, when the lighting load 208 is on, lightintensity level may range from 1% to substantially 100%.

A simplified block diagram of the dimmer switch 202 and the remoteswitch 204 of the multiple location lighting control system 200 is shownin FIG. 4. The dimmer switch 202 employs a semiconductor switch 420coupled between the hot terminal H and the dimmed hot terminal DH, tocontrol the current through, and thus the light intensity of, thelighting load 208. The semiconductor switch 420 may be implemented as atriac or two field effect transistors (FETs) in anti-series connection.The semiconductor switch 420 has a control input (or gate), which isconnected to a gate drive circuit 424. The input to the gate will renderthe semiconductor switch 420 conductive or non-conductive, which in turncontrols the power supplied to the lighting load 208. The gate drivecircuit 424 provides control inputs to the semiconductor switch 420 inresponse to command signals from a microcontroller 426.

The microcontroller 426 generates command signals to a visual display,e.g., a plurality of LEDs 418, for feedback to the user of the dimmerswitch 202. The microcontroller 426 receives inputs from a zero-crossingdetector 430 and a signal detector 432. A power supply 428 generates aDC output voltage V_(CC) to power the microcontroller 426. The powersupply is coupled between the hot terminal H and the dimmed hot terminalDH.

The zero-crossing detector 430 determines the zero-crossings of theinput AC waveform from the AC power supply 206. A zero-crossing isdefined as the time at which the AC supply voltage transitions frompositive to negative polarity, or from negative to positive polarity, atthe beginning of each half-cycle. The zero-crossing information isprovided as an input to microcontroller 426. The microcontroller 426provides the gate control signals to operate the semiconductor switch420 to provide voltage from the AC power supply 206 to the lighting load208 at predetermined times relative to the zero-crossing points of theAC waveform.

Generally, two techniques are used for controlling the power supplied tothe lighting load 208: forward phase control dimming and reverse phasecontrol dimming. In forward phase control dimming, the semiconductorswitch 420 is turned on at some point within each AC line voltagehalf-cycle and remains on until the next voltage zero-crossing. Forwardphase control dimming is often used to control energy to a resistive orinductive load, which may include, for example, a magnetic low-voltagetransformer or an incandescent lamp. In reverse phase control dimming,the semiconductor switch 420 is turned on at the zero-crossing of the ACline voltage and turned off at some point within each half-cycle of theAC line voltage. Reverse phase control is often used to control energyto a capacitive load, which may include, for example, an electroniclow-voltage transformer. Since the semiconductor switch 420 must beconductive at the beginning of the half-cycle, and be able to be turnedoff with in the half-cycle, reverse phase control dimming requires thatthe dimmer have two FETs in anti-serial connection, or the like.

The signal detector 432 has an input 440 for receiving switch closuresignals from momentary switches T, R, and L. Switch T corresponds to atoggle switch controlled by the switch actuator 316, and switches R andL correspond to the raise and lower switches controlled by the upperportion 314A and the lower portion 314B, respectively, of the intensityselection actuator 314.

Closure of switch T will connect the input of the signal detector 432 tothe DH terminal of the dimmer switch 202, and will allow both positiveand negative half-cycles of the AC current to flow through the signaldetector. Closure of switches R and L will also connect the input of thesignal detector 432 to the DH terminal. However, when switch R isclosed, current can only flow through the signal detector 432 during thepositive half-cycle of the AC power supply 406 because of a diode 434.In similar manner, when switch L is closed, current can only flowthrough the signal detector 432 during the negative half-cycles becauseof a diode 436. The signal detector 432 detects when the switches T, R,and L are closed, and provides two separate output signalsrepresentative of the state of the switches as inputs to themicrocontroller 426. A signal on the first output of the signal detector432 indicates a closure of switch R and a signal on the second outputindicates a closure of switch L. Simultaneous signals on both outputsrepresents a closure of switch T. The microprocessor controller 426determines the duration of closure in response to inputs from the signaldetector 432.

The remote switch 204 provides a means for controlling the dimmer switch202 from a remote location in a separate wall box. The remote switch 204includes a further set of momentary switches T′, R′, and L′ and diodes434′ and 436′. A wire connection is made between the AD terminal of theremote switch 204 and the AD terminal of the dimmer switch 202 to allowfor the communication of actuator presses at the remote switch. The ADterminal is connected to the input 440 of the signal detector 432. Theaction of switches T′, R′, and L′ in the remote switch 204 correspondsto the action of switches T, R, and L in the dimmer switch 202.

The system shown in FIGS. 2, 3, and 4 provides a fully functionalthree-way switching system wherein the user is able to access allfunctions, such as, for example, dimming at both locations. However, inorder to provide this functionality, both switching devices need to bereplaced with the respective devices 202, 204.

Sometimes it is desired to place only one smart switch in the three-wayor four-way switching circuit. As shown in FIG. 1B, it is not possibleheretofore to do this by simply replacing the dimmer 152 with a smartdimmer, leaving mechanical three-way switch 104 in the circuit becausewhen switch 104 breaks the circuit, power no longer is provided to themicrocontroller of the smart dimmer (in place of the dimmer 152) becausecurrent no longer flows through the dimmer to the lighting load 108. Thethree-way and four-way dimmer switch according to the present inventionprovides a solution to this problem and also optionally provides a meansfor remote control of the switch.

In one prior art remote control lighting control system, a singlemulti-location dimmer and up to nine “accessory” dimmers can beinstalled on the same circuit to enable dimming from a plurality ofcontrols. In the prior art, accessory dimmers are necessary becauseprior art multi-location dimmers are incompatible with mechanicalthree-way switches. Accessory dimmers installed throughout a house cangreatly increase the cost of the components and of the installation of adimming system.

Moreover, even though the multiple location lighting control system 200allows for the use of a smart dimmer switch in a three-way system, it isnecessary for the customer to purchase the remote switch 204 along withthe smart dimmer switch 202. Often, the typical customer is unaware thata remote switch is required when buying a smart dimmer switch for athree-way or four-way system until after the time of purchase when thesmart dimmer switch is installed and it is discovered that the smartdimmer switch will not work properly with the existing mechanicalthree-way or four-way switch. Therefore, there exists a need for a smartdimmer that may be installed in any location of a three-way or four-waysystem without the need to purchase and install a special remote switch.

A smart three-way switch has also been designed that operates with aconventional mechanical three-way switch, but that system requiresrewiring of the mechanical three-way switch in order to provide properthree-way operation from both locations. This is the subject of commonlyassigned U.S. patent application Ser. No. 11/125,045, filed May 9, 2005,entitled DIMMER FOR USE WITH A THREE-WAY SWITCH, which is incorporatedherein by reference in its entirety.

SUMMARY OF THE INVENTION

The present invention improves upon these and other shortcomingsidentified above, particularly with respect to the existing smartthree-way and four-way dimmer switches, providing smart dimmer switchesthat can replace existing mechanical three-way and four-way switches andbeing fully operational with existing mechanical three-way and four-wayswitches without requiring rewiring or replacement of the otherswitches.

According to the present invention, a dimmer switch for controlling theamount of power delivered from an AC power source to an electrical loadis adapted to be coupled either to a circuit including a single-poledouble-throw three-way switch or to a circuit including an accessorydimmer. The dimmer switch comprises first, second, and third electricalload terminals, an accessory dimmer connection, a controllablyconductive device, a sensing device, a controller, and a power supply.The controllably conductive device is electrically coupled to the first,second, and third load terminals. The controllably conductive device hasa conductive state in which the controllably conductive device iscontrolled so as to deliver a desired amount of power to the load and anon-conductive state in which the controllably conductive device iscontrolled so as to deliver substantially no power to the load. Thecontrollably conductive device is arranged such that when thecontrollably conductive device is in the conductive state, and thedimmer switch is coupled to the circuit, a current to the load flowsbetween the first terminal and the second terminal or between the firstterminal and the third terminal. The sensing device is electricallycoupled to at least one of the second load terminal and the third loadterminal and is operable to sense an electrical characteristicassociated with the load terminal to which the sensing device iscoupled. The controller is operably operatively coupled to thecontrollably conductive device, the sensing device, and the accessorydimmer connection. The power supply is electrically coupled in shuntelectrical connection with the controllably conductive device andoperable to provide power to the controller. The controller is operableto control the controllably conductive device in response to either anoutput of the sensing device in accordance with the electricalcharacteristic or a control signal provided to the accessory dimmerconnection.

According to another embodiment of the present invention, the dimmerswitch further comprises a fourth load terminal and a second sensingdevice electrically coupled between the third load terminal and thefourth load terminal and adapted to carry the load current through thefourth load terminal. The first and second sensing devices preferablycomprise current sensing devices operable to generate first and secondcontrol signals, respectively. The first control signal isrepresentative of whether a first current is flowing through the secondload terminal, and the second control signal is representative ofwhether a second current is flowing through the third load terminal. Thedimmer switch further comprises a signal detector electrically coupledto the accessory dimmer connection and operable to provide in responseto the control signal an indication of a command to control theelectrical load. The controller is operably coupled to the controllablyconductive device, the first and second current sensing devices, and thesignal detector. The controller is operable to control the controllablyconductive device either in response to the first and second controlsignals of the first and second current sensing devices, respectively,or the accessory control signal provided to the accessory dimmerconnection.

In addition, the present invention provides a method for controlling theamount of power delivered to an electrical load form an AC power source.The method comprises the steps of: (1) providing first, second, andthird electrical load terminals; (2) providing an accessory connection;(3) electrically coupling a controllably conductive device to the first,second, and third load terminals, the controllably conductive devicehaving a conductive state in which the controllably conductive device iscontrolled so as to deliver a desired amount of power to the load and anon-conductive state in which the controllably conductive device iscontrolled so as to deliver substantially no power to the load; (4)sensing an electrical characteristic associated with at least one of thesecond load terminal and the third load terminal; (5) controlling thecontrollably conductive device in accordance with the sensed electricalcharacteristic, such that a current through the load flows between thefirst load terminal and the second load terminal, or between the firstload terminal and the third load terminal; (6) receiving a controlsignal via the accessory terminal; and (7) controlling the controllablyconductive device in accordance with the received control signal.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form, which is presently preferred, it being understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown. The features and advantages of the presentinvention will become apparent from the following description of theinvention that refers to the accompanying drawings, in which:

FIG. 1A shows a prior art three-way switch system, which includes twothree-way switches;

FIG. 1B shows an example of a prior art three-way dimmer switch systemincluding one prior art three-way dimmer switch and one three-wayswitch;

FIG. 1C shows a prior art four-way switching system;

FIG. 1D shows a prior art extended four-way switching system;

FIG. 2 is a simplified block diagram of a typical prior art multiplelocation lighting control system;

FIG. 3 shows the prior art user interface of the dimmer switch of themultiple location lighting control system of FIG. 2;

FIG. 4 is a simplified block diagram of the dimmer switch and the remoteswitch of the prior art multiple location lighting control system ofFIG. 2;

FIG. 5A is a simplified block diagram of a three-way lighting controlsystem including a smart three-way dimmer according to the presentinvention;

FIG. 5B shows a state diagram summarizing the operation of the lightingcontrol system of FIG. 5A;

FIG. 5C is a perspective view of a user interface of the smart three-waydimmer of FIG. 5A;

FIG. 6A is a simplified block diagram of a three-way lighting controlsystem including a second embodiment of a smart three-way dimmeraccording to the present invention;

FIG. 6B is a simplified schematic diagram of a first detect circuit ofthe dimmer of FIG. 6A;

FIG. 7A is a simplified block diagram of a three-way lighting controlsystem including a third embodiment of a smart three-way dimmeraccording to the present invention;

FIG. 7B shows a simplified schematic diagram of a current detect circuitof the dimmer of FIG. 7A;

FIG. 8 is a simplified block diagram of a four-way lighting controlsystem including a smart four-way dimmer according to the presentinvention;

FIG. 9 shows a state diagram summarizing the operation of the lightingcontrol system of FIG. 8;

FIG. 10 is a flowchart of a control loop of the controller of the smartfour-way dimmer of FIG. 8 for determining the state of the dimmer;

FIG. 11 is a flowchart of the process of the button routine of thecontrol loop of FIG. 10;

FIG. 12 is a flowchart of the process of the current detect routine ofthe control loop of FIG. 10;

FIG. 13 is a flowchart of the process of the triac state routine of thecontrol loop of FIG. 10;

FIG. 14 is a flowchart of the startup process of the controller of thedimmer switch of FIG. 8;

FIG. 15 is a simplified block diagram of a smart multi-location dimmeroperable to be coupled in a three- or four-way system, or in amulti-location lighting control system;

FIG. 16A is a simplified block diagram of a four-way system comprisingthe dimmer of FIG. 15;

FIG. 16B is a simplified block diagram of a multi-location lightingcontrol system comprising the dimmer of FIG. 15;

FIG. 17 is a state diagram summarizing the operation of themulti-location dimmer of FIG. 15; and

FIG. 18 is a rear perspective view of the multi-location dimmer of FIG.15.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 5A is a simplified block diagram of a three-way lighting controlsystem 500 including a smart three-way dimmer switch 502 according tothe present invention. The dimmer 502 and a standard three-way switch504 are connected in series between an AC voltage source 506 and alighting load 508. The dimmer 502 includes a hot terminal H that iscoupled to the AC voltage source 506 and two dimmed hot terminals DH1,DH2 that are connected to the two fixed contacts of the three-way switch504. The common terminal of the three-way switch 504 is coupled to thelighting load 508. Alternatively, the dimmer 502 could be connected onthe load-side of the system 500 with the three-way switch 504 on theline-side. The dimmer 502 can be installed to replace an existingthree-way switch without the need to replace the other existingthree-way switch 504, and without the need for a wiring change to thethree-way switch being replaced. The terminals H, DH1, DH2 of the dimmer502 may be screw terminals, insulated wires or “flying leads”, stab-interminals, or other suitable means of connecting the dimmer to the ACvoltage source 506 and the lighting load 508.

In this embodiment of the smart two-wire dimmer switch 502, twobidirectional semiconductor switches 510, 514 are used. The dimmer 502implements each semiconductor switch as a triac. However, othersemiconductor switching circuits may be used, such as, for example, twoFETs in anti-series connection, or an insulated-gate bipolar junctiontransistor (IGBT). A first triac 510 is connected in series between thehot terminal H and the first dimmed hot terminal DH1. The first triac510 has a gate (or control input) that is coupled to a first gate drivecircuit 512. A second triac 514 is connected in series between the hotterminal H and the second dimmed hot terminal DH2 and has a gate that iscoupled to a second gate drive circuit 516. The dimmer 502 furtherincludes a controller 518 that is coupled to the gate drive circuits512, 516 to control the conduction times of the triacs 510, 514 eachhalf-cycle. The controller 518 is preferably implemented as amicrocontroller, but may be any suitable processing device, such as aprogrammable logic device (PLD), a microprocessor, or an applicationspecific integrated circuit (ASIC).

A power supply 520 generates a DC voltage, V_(CC), to power thecontroller 518. The power supply 520 is coupled from the hot terminal Hto the first dimmed hot terminal DH1 through a first diode 522 and tothe second dimmed hot terminal DH2 through a second diode 524. Thisallows the power supply 520 to draw current through the first dimmed hotterminal DH1 when the three-way switch 504 is in position A and throughthe second dimmed hot terminal DH2 when the three-way switch 504 is inposition B. The power supply 520 is able to charge when the triacs 510,514 are both not conducting and there is a voltage potential developedacross the dimmer 502.

The dimmer 502 further includes a zero-crossing detector 526 that isalso coupled between the hot terminal H and the dimmed hot terminalsDH1, DH2 through the diodes 522, 524, respectively. The zero-crossingdetector 526 provides a control signal to the controller 518 thatidentifies the zero-crossings of the AC supply voltage. The controller518 determines when to turn on the triacs 510, 514 each half-cycle bytiming from each zero-crossing of the AC supply voltage.

A user interface 528 is coupled to the controller 518 and to allow auser to determine a desired lighting level (or state) of the lightingload 508. The user interface 528 provides a plurality of actuators forreceiving inputs from a user. For example, the user interface 528 maycomprise a toggle button 560 (i.e., a tap switch) and an intensityactuator 570 (i.e., a slider control) as shown in FIG. 5C. In responseto an actuation of the toggle button 560, the controller 518 will togglethe state of the lighting load 508 (i.e., from on to off and vice versa)by changing which one of the two triacs 510, 514 is conducting. Thecontroller 518 drives the triacs 510, 514 conduct on a complementarybasis, such that only one of the two triacs operable to conduct at asingle time. In this way, the dimmer 502 operates similarly to astandard SPDT switch by allowing current to either flow through thefirst dimmed hot terminal DH1 or the second dimmed hot terminal DH2solely in response to an actuation of the toggle button 560.Alternatively, the user interface 528 may include a separate on buttonand off button, which will cause the lighting load 508 to turn on andoff, respectively. Movement of the intensity actuator 570 will cause thedimmer 502 to control the intensity of the lighting load 508. The dimmer502 further includes an airgap switch 530 for preventing current flowingthrough either of the triacs 510, 514, and an inductor 531 for providingelectromagnetic interference (EMI) filtering.

When the three-way switch 504 is in position A and the desired state ofthe lighting load 508 is on, the controller 518 will turn the firsttriac 510 on for a portion of each half-cycle, while maintaining thesecond triac 514 in the non-conducting state. If the three-way switch504 is then toggled from position A to position B, current will not flowto the lighting load 508 since the second triac 514 is not conducting.Therefore, the lighting load 508 will not be illuminated. Alternatively,if the three-way switch 504 is in position A, the lighting load 508 ison, and the toggle button of the user interface 528 is actuated, thecontroller 518 will cause the first triac 510 to stop conducting and thesecond triac 514 to begin conducting. The lighting load 508 will be offbecause the controller 518 is driving the second triac 514 while thethree-way switch 504 is in position A. If the toggle button of the userinterface 528 is actuated again, the controller 518 will stop drivingthe second triac 514 and will cause the first triac 510 to beginconducting, thus causing the lighting load 508 to illuminate again.

Similarly, when the three-way switch 504 is in position B and thedesired state of the lighting load 508 is on, the controller 518 willturn the second triac 514 on for a portion of each half-cycle, whilemaintaining the first triac 510 in the non-conducting state. If thethree-way switch 504 is then switched to position A, the current path tothe lighting load 508 is interrupted and the lighting load will be off.Also, if the three-way switch 504 is in position B, the lighting load508 is on, and the toggle button of the user interface 528 is actuated,the controller 528 will cause the second triac 514 to stop conductingand the first triac 510 to begin conducting. The lighting load 508 willbe off because the first triac 510 is conducting and the three-wayswitch 504 is in position B.

The power supply 520 preferably has a large enough storage capacitor topower the controller 518 during the times when the three-way switch 504is transitioning from position A to position B and vice versa. Forexample, as the three-way switch 504 is toggled, current temporarilywill not flow through either of the dimmed hot terminals DH1, DH2 as themovable contact transitions and the power supply 520 will provide powerto the controller 518 by virtue of the internal storage capacitor. Theamount of power that the power supply 504 needs to provide when thethree-way switch 504 is transitioning is dependent on the transitioningtime required for the movable contact to move from one fixed contact tothe other.

However, it is not always possible to guarantee that the power supply520 will be able to power the controller 518 and other low voltagecircuitry during the time when the three-way switch 504 is transitioningbetween positions. Because of space limitations in a wall-mountabledimmer switch, it is not possible to simply include a particularly largestorage capacitor in the power supply 520 to provide power during thetransitioning time. Also, since the transitioning time is dependent onthe force that a user exerts on the actuator of the three-way switch504, the transitioning time can vary widely from one transition to thenext. All three-way switches 504 include a region of “dead travel”,i.e., when the movable contact of the three-way switch is approximatelyhalf way between position A and position B and is not contacting eitherof the fixed contacts. Sometimes, it is possible for the three-wayswitch 504 to be sustained in the region of dead travel, such that nocurrent may flow through the power supply 520 for an indeterminateperiod of time.

Accordingly, the dimmer 502 includes a memory 532 that enables thedimmer 502 to return to the appropriate state, i.e., to control thecorrect one of the two triacs 510, 514, if power to the dimmer 502 istemporarily lost when the three-way switch 504 is transitioning. Thememory 532 is coupled to the controller 518. Whenever the toggle buttonof the user interface 528 is actuated, the controller 518 stores in thememory 532, which one of the triacs 510, 514 is presently beingcontrolled. In this way, if dimmer 502 temporarily loses power and theDC voltage V_(CC) falls below a level that allows for proper operationof the controller 518, the controller will read from the memory 532which triac 510, 514 to control at “power up”, i.e. when the DC voltageV_(CC) rises back above the level that ensures proper operation of thecontroller.

FIG. 5B shows a state diagram 550 summarizing the operation of thelighting control system 500 of FIG. 5A. Two states 552, 554 are shown inwhich the lighting load 508 will be on since the three-way switch 504 isin the correct position to complete the circuit through the conductingtriac. For example, at state 552, when the three-way switch 504 is inposition A, the first triac 510 is able to conduct current to thuscontrol the lighting load 508. The state diagram 550 also includes twostates 556, 558 in which the lighting load 508 will be off since thethree-way switch 504 is not in a position to conduct current through thetriac that is enabled for conduction. A transition between states can becaused by one of three actions: a toggle of the three-way switch 504from position A to position B (designated by ‘B’ in FIG. 5B), a toggleof the three-way switch 504 from position B to position A (designated by‘A’), and an actuation of the toggle switch of the user interface 528(designated by ‘T’).

FIG. 6A shows a simplified block diagram of a three-way lighting controlsystem 600 including a second embodiment of a smart three-way dimmerswitch 602 according to the present invention. A first detect circuit(or sensing circuit) 636 is coupled across the first triac 510 and asecond detect circuit (or sensing circuit) 638 is coupled across thesecond triac 514. The detect circuits 636, 638 provide control signalsto the controller 618 representative of electrical characteristics ofthe first dimmed hot terminal DH1 and the second dimmed hot terminalDH2, respectively. Each of the electrical characteristics may be avoltage developed across one of the respective triacs. Alternatively,the detect circuits 636, 638 may be placed in series with the dimmed hotterminals DH1, DH2 and the electrical characteristics may be currentsthrough the dimmed hot terminals. In essence, the sensing of theelectrical characteristics provides a determination of whether a path ofcontinuity exists between hot and neutral of the AC voltage source 506through the lighting load 508, the three-way switch 504, and thethree-way dimmer switch 602, at either the first dimmed hot terminal DH1or the second dimmed hot terminal DH2.

The controller 618 uses this information to determine the position ofthe three-way switch 504 in the system 600. For example, when thethree-way switch 504 is in position A and the first triac 510 isnon-conductive, a voltage will develop across the first detect circuit636, which will output a signal indicating that the three-way switch 504is in position A. Similarly, when the three-way switch 504 is inposition B, the second detect circuit 638 will output a correspondingsignal to the controller 618. The controller 618 uses the information ofthe state of the three-way switch 504 to provide feedback to the uservia a plurality of LEDs on a user interface 628 and may provide feedbackinformation to other control devices via an optional communicationcircuit 634. For example, the user interface 628 may be the same as theuser interface shown in FIG. 3.

The communication circuit 634 may be coupled to a communications link,for example, a wired serial control link, a power-line carrier (PLC)communication link, or a wireless communication link, such as aninfrared (IR) or a radio frequency (RF) communication link. An exampleof an RF lighting control system is described in commonly assigned U.S.Pat. No. 5,905,442, issued May 18, 1999, entitled METHOD AND APPARATUSFOR CONTROLLING AND DETERMINING THE STATUS OF ELECTRICAL DEVICES FROMREMOTE LOCATIONS.

Instead of providing complementary control of the triacs 510, 514, thecontroller 618 could control the triacs to the same state at the sametime. For example, when the first triac 510 is conducting and the secondvoltage detect circuit 638 determines that the three-way switch 504 hasbeen toggled to position B, the controller could cause both triacs tostop conducting since the desired lighting level of the lighting load508 is off. When neither triac 510, 514 is conducting, substantially nopower, i.e., only an amount of power that will not illuminate thelighting load 508, is conducted to the lighting load.

Accordingly, the controller is operable to detect a change of theposition of the three-way switch 504 and can determine when to togglepower to the load based on the three-way switch position change and thepresent state of the dimmer. Thus, the embodiments shown in FIGS. 5A and6A are compatible with a mechanical three-way switch 504.

FIG. 6B is a simplified schematic diagram of a possible implementationof the first detect circuit 636. Since the voltage provided across thedetect circuit 636 is an AC line voltage, the detect circuit includes anoptocoupler 640. A resistor 642 is provided in series with thephotodiodes 640A, 640B of the optocoupler 640 to limit the currentthrough the photodiodes. The voltage at the collector of thephototransistor 640C of the optocoupler 640 is provided to thecontroller 618. A resistor 646 is provided in series with thephototransistor 640C to pull the voltage provided to the controller 618up to the DC voltage VCC of the power supply 520 when thephototransistor is not conducting (i.e., when there is no voltage acrossthe detect circuit 636).

When a voltage is produced across the detect circuit 636, current flowsthrough the photodiode 640A in the positive half-cycles and thephotodiode 640B in the negative half-cycles. Hence, the phototransistor640C conducts and the voltage at the collector of the phototransistor ispulled down to a circuit common 648. The schematic diagram of the seconddetect circuit 638 is identical to the schematic diagram of the firstdetect circuit 636 shown in FIG. 6B, differing only in the fact that thesecond detect circuit 638 is connected between the hot terminal H andthe second dimmed hot terminal DH2. Alternatively, the first and seconddetect circuits 636, 638 could be implemented as a simple resistivecircuit (not shown), for example, a resistor divider, with thecontroller 518 operable to detect a voltage produced by the resistivecircuit.

FIG. 7A shows a simplified block diagram of a three-way lighting controlsystem 700 including a third embodiment of a smart three-way dimmerswitch 702 according to the present invention. In this embodiment, thedimmer switch 702 includes a single controllably conductive device, forexample, a bidirectional semiconductor switch, such as a triac 710. Acontroller 714 is coupled to the gate of the triac 710 through a gatedrive circuit 712 and controls the conduction time of the triac eachhalf-cycle. A power supply 716 is coupled across the triac 710 andgenerates a DC voltage VCC to power the controller 714. A zero-crossingdetector 718 determines the zero-crossing points of the AC voltagesource 506 and provides this information to the controller 714. A userinterface 720 provides inputs to the controller 714 from a plurality ofbuttons (including a toggle button) and includes a plurality of LEDs forfeedback to a user. A communication circuit 722 allows the controller714 to transmit and receive messages with other control devices. Anairgap switch 724 disconnects the dimmer switch 702 and the lightingload 508 from the AC voltage source 506. An inductor 725 is in serieswith the triac 710 and provides EMI filtering. A memory 726 stores thepresent state of the dimmer switch 702, such that the controller 714 canproperly operate the triac 710 at power up.

The dimmer 702 also includes a current detect circuit (sensing circuit)728 that is coupled between the first dimmed hot terminal DH1 and thesecond dimmed hot terminal DH2. The current detect circuit 728 isoperable to detect when there is current flowing through the seconddimmed hot terminal DH2 and to accordingly provide a control signal tothe controller 714. The power supply 716 provides a current path throughthe current detect circuit 728 when the triac 710 is non-conducting.When the three-way switch 504 is in position B, the charging currentthrough the power supply 716 will flow through the second dimmed hotterminal DH2. The current detect circuit 728 will sense the chargingcurrent and indicate to the controller 714 that the three-way switch isin position B. When the three-way switch 504 is in position A, nocurrent will flow through the current detect circuit 728 and no signalwill be provided to the controller 714. Thus, the controller 714 is ableto determine the state of the three-way switch 504 and to control thestate of the lighting load 508 (i.e., on or off) accordingly.

The memory 726 stores the state of the triac 710 and of the three-wayswitch 504. If the power supply 716 is unable to supply power to thecontroller 714 through the duration of a transition of the three-wayswitch 504, the controller 714 will reset, i.e., power down and thenpower up when the three-way switch 504 has finished the transition. Atpower up, the controller 714 of the dimmer 702 checks the status of thethree-way switch 504 from the control signal of the current detectcircuit 728 and compares the present state of the three-way switch tothe state of the three-way switch that is stored in the memory 726. Ifthe status of the three-way switch 504 has changed, the controller 714will toggle the state of the triac 710 based on the present state of thetriac that is stored in the memory 726.

FIG. 7B shows a simplified schematic diagram of the current detectcircuit (sensing circuit) 728 of the dimmer 702. The current detectcircuit 728 includes a current sense transformer 730 that has a primarywinding coupled in series between the dimmed hot terminals DH1, DH2. Thecurrent sense transformer 730 only operates above a minimum operatingfrequency, for example, 100 kHz, such that current only flows in thesecondary winding when the current waveform through the primary windinghas a frequency above the minimum operating frequency. The current sensetransformer 730 detects the falling edge of the current waveform throughthe power supply 716 when the charging current flows through the seconddimmed hot terminal DH2. Since the dimmer 702 is using a triac as thesemiconductor switch, the dimmer operates using forward phase controldimming, in which the triac 710 is non-conductive at the beginning ofeach half-cycle. Thus, the power supply 716 charges at the beginning ofeach half-cycle. When the power supply 716 stops charging during ahalf-cycle, the charging current through the power supply will drop tozero. Since the falling time of the current waveform through the primarywinding of the current sense transformer 730 is very short (i.e., thewaveform has a high-frequency component), a current will flow in thesecondary of the current sense transformer when the switch 504 is inposition B. An example of the current sense transformer 730 is partnumber CT319-200, manufactured by Datatronic, Ltd.

The secondary winding of the current sense transformer 730 is coupledacross a resistor 732. The resistor 732 is further coupled betweencircuit common and the negative input of a comparator 734. A referencevoltage is produced by a voltage divider comprising two resistors 736,738 and is provided to the positive input of the comparator 734. Theoutput of the comparator 734 is tied to V_(CC) through a resistor 740and is coupled to the controller 714. When current flows through thesecondary winding of the current sense transformer 730, a voltage isproduced across the resistor 732 that exceeds the reference voltage. Thecomparator 734 then drives the output low, signaling to the controller714 that current has been sensed. Alternatively, the current detectcircuit 728 may be implemented using an operational amplifier or adiscrete circuit comprising one or more transistors rather than thecomparator 734.

FIG. 8 is a simplified block diagram of a four-way lighting controlsystem 800 including a smart four-way dimmer switch 802 according to thepresent invention. The dimmer 802 and two three-way switches 803, 804are coupled between an AC voltage source 806 and a lighting load 808.The dimmer 802 has replaced the four-way switch 185 in the four-waylighting control system 180 of FIG. 1C.

The dimmer 802 operates on the same principles as the dimmer 702 of FIG.7A. However, the dimmer 802 includes an additional hot terminal H2 thatis coupled to the three-way switch 803 on the line-side of the system802. The dimmer 802 further comprises a second current detect circuit(sensing circuit) 829 that is coupled between the hot terminals H, H2and provides a signal to a controller 814. The second current detectcircuit 829 operates in the same manner as the first current detectcircuit 728. When current is detected flowing through the second currentdetect circuit 829, the controller 814 determines that the line-sidethree-way switch 803 is in position D. When no current is flowingthrough the second current detect circuit 829, the three-way switch 803is in position C. Thus, the controller 814 is able to determine thestates of both the line-side three-way switch 803 and the load-sidethree-way switch 804 and to operate the triac 710 accordingly. Wheneither three-way switch 803, 804 is toggled, or the toggle button of theuser interface 720 is actuated, the controller 714 will toggle the stateof the lighting load 808.

Even though the four-way dimmer switch 802 has four connections, thedimmer could be installed in a three-way system (in place of thethree-way dimmer switch 502 in FIG. 5A or three-way dimmer switch 702 inFIG. 7A). One of the additional terminals DH2 or H2 would not beconnected in the system 800. So, the dimmer 802 allows for a singledevice that can be installed in any location of a four-way or three-waysystem without the need to determine in advance what kind of switch thedimmer will be replacing.

FIG. 9 shows a state diagram 900 summarizing the operation of thelighting control system 800 of FIG. 8. In four states 902, 904, 906,908, the triac 710 will be conducting since the desired state of thelighting load 808 is on. The state diagram 900 also shows four states912, 914, 916, 918 in which the desired state of the lighting load 808is off. A transition between states can be caused by one of fiveactions: a toggle of the three-way switch 804 from position A toposition B (designated by ‘B’ in FIG. 6B), a toggle of the three-wayswitch 804 from position B to position A (designated by ‘A’), a toggleof the three-way switch 803 from position C to position D (designated by‘D’), a toggle of the three-way switch 803 from position D to position C(designated by ‘C’), and an actuation of the toggle switch of the userinterface 720 (designated by ‘T’) (or when a “toggle” signal is receivedvia the communication circuit 722). Note that in all states of the statediagram 900, the triac 710 is operable to conduct current to thelighting load 808 to control the state of the lighting load independentof the states of the three-way switches 803, 804.

The state diagram 900 thus identifies the status of the three-way switch803, the three-way switch 804, and the triac 710 (and thus the lightingload 808) for all possible states and shows all the state transitionswhen the three-way switches 803, 804 are toggled and the toggle buttonof the user interface 720 is actuated (or when a “toggle” signal isreceived via the communication circuit 722).

FIG. 10 is a flowchart of a state control procedure 1000 of thecontroller 814 for determining the state of the dimmer 802. The statecontrol procedure 1000 runs periodically, for example, approximatelyevery 6 msec. The state control procedure 1000 includes a button routine1100, a current detect routine 1200, and a triac state routine 1300.While the button routine 1100, the current detect routine 1200, and thetriac state routine 1300 are shown executing in sequential order in FIG.10, these routines alternatively could each be called from differentpieces of software and each be executed at a different interval.

The controller 814 utilizes a FIFO (first in, first out) stack to storerequests for the triac state routine 1300 to change the state of thetriac 710. The button routine 1100 and the current detect routine 1200are both operable to load an event (for example, a “toggle event”) intothe FIFO stack. The triac state routine loads these events from the FIFOstack and processes the events. In the discussion of FIGS. 10 through14, only toggle events are discussed. However, other events, such as“increase intensity” or “decrease intensity”, could be loaded into theFIFO stack by other routines (not described).

In the state control procedure 1000, the controller 814 utilizes threevariables: TRIAC_STATUS, 1ST_DETECT, and 2ND_DETECT that are stored inthe memory 726. The variable TRIAC_STATUS stores the conduction state ofthe triac 710, i.e., either ON or OFF. The variables 1ST_DETECT and2ND_DETECT store the state of the first current detect circuit 728 andthe second current detect circuit 829, respectively. The possible valuesfor the variables 1ST_DETECT and 2ND_DETECT are TRUE (when current isdetected) and FALSE (when current is not detected).

A flowchart describing the process of the button routine 1100 is shownin FIG. 11. At step 1110, the controller 814 first checks the togglebutton of the user interface 720. If the toggle button is being pressedat step 1112, the controller 814 will load a “toggle event” into theFIFO stack at step 1114 and exit the process. If the toggle button isnot being pressed at step 1112, the process simply exits.

FIG. 12 is a flowchart of the process of the current detect routine1200. The outputs of the first current detect circuit 728 and secondcurrent detect circuit 829 are coupled to separate interrupt inputs onthe controller 814. Whenever an input is provided from the first currentdetect circuit 728, a first interrupt routine is executed to set a firstcurrent detect flag. Similarly, whenever an input is provided from thefirst current detect circuit 728, a second interrupt routine is executedto set a second current detect flag.

Referring to FIG. 12, the first current detect flag is first checked atstep 1210. At step 1212, if the first current detect flag has changedstates, i.e., the new state of the first current detect circuit is notequal to the value stored in the variable 1ST_DETECT, the process movesto step 1214, where a determination is made as to whether the presentvalue of the variable 1ST_DETECT is equal to TRUE. If so, the variable1ST_DETECT is set to FALSE at step 1216; otherwise, the variable1ST_DETECT is set to TRUE at step 1218. Next, the controller 814 willload a “toggle event” into the FIFO stack at step 1220.

After loading a toggle event into the FIFO stack at step 1220, or afterdetecting no change of state of the first current detect circuit 728 atstep 1212, the output of the second current detect circuit 829 ischecked at step 1222. At step 1224, if the output of the second currentdetect circuit 829 has changed states, i.e., the new state of the secondcurrent detect circuit is not equal to the value stored in the variable2ND_DETECT, a determination is made as to whether the present value ofthe variable 2ND_DETECT is equal to TRUE at step 1226. If so, thevariable 2ND_DETECT is set to FALSE at step 1228; otherwise, thevariable 2ND_DETECT is set to TRUE at step 1230. Next, the controller714 will load a toggle event into the FIFO stack at step 1232 and exit.

At step 1224, if the output of the second current detect circuit 829 hasnot changed states, then the process simply exits without loading atoggle event into the FIFO stack.

FIG. 13 is a flowchart of the process of the triac state routine 1300.First, a toggle event is loaded from the FIFO stack (and deleted fromthe stack at the same time) at step 1310. If there is a toggle event inthe FIFO stack to handle at step 1312, the triac state will be toggled.At step 1314, if the variable TRIAC_STATE is equal to OFF, then thevariable TRIAC_STATE is set to ON at step 1316. Otherwise, the variableTRIAC_STATE is set to OFF at step 1318. At step 1320, the variablesTRIAC_STATE, 1ST_DETECT, and 2ND_DETECT are stored in the memory 726.The process loops until there are no toggle events to handle at step1312, at which time the process exits.

FIG. 14 is a flowchart of the startup process 1400 that the controller814 performs at power up, for example, if the controller 814 loses powerwhile a connected three-way or four-way switch is transitioning. First,the controller 814 reads the variables TRIAC_STATE, 1ST_DETECT, and2ND_DETECT from the memory 726 at step 1410. Next, the controller 814checks the status of the first current detect circuit 728 and the secondcurrent detect circuit 829 in the current detect routine 1100. Next, thecontroller 814 determines whether to change the variable TRIAC_STATE inthe triac state routine 1200. Finally, the process exits to begin normaloperation executing the state control procedure 1000 of FIG. 10.

Although the embodiment of FIG. 8 shows two current detect circuits 728,829. Additional sensing circuits could be employed. For example, acurrent detect circuit could be employed coupled in series with eachterminal of the smart four-way dimmer switch 802 for a total of fourcurrent detect circuits.

The smart dimmers 502, 602, 702, and 802 are useful in three-way andfour-way applications without the requirement of replacing the standardswitches already installed in the other switching location(s). Unlikeapplications described above in the prior art, all other switches atother switching locations in the same three-way or four-way circuit donot have to be replaced with an accessory dimmer. Accordingly, thepresent invention has a reduced cost. Only one smart three-way orfour-way dimmer need be purchased and the existing switches in thethree-way or four-way switching circuit remain fully operational. Byinstalling a single dimmer 502, 602, 702, or 802, less time is requiredfor installation, thereby reducing installation costs. Also, there isless chance of errors in installation (e.g., mistakes in wiring),further reducing installation costs and the likelihood of damaging andreplacing units.

However, it is still desirable to allow a user to control the smartdimmers 502, 602, 702, and 802 from an accessory dimmer (e.g., theaccessory dimmer 204 shown in FIG. 2). FIG. 15 is a simplified blockdiagram of a smart multi-location dimmer 1502 operable to be coupled ina three- or four-way system (as described in the present invention) orin a multi-location lighting control system, such as the prior artmultiple location lighting control system 200 shown in FIG. 2. Themulti-location dimmer 1502 comprises four load terminals H1, H2, DH1,DH2 and an accessory dimmer connection AD. A controller 1514 receivesinputs from the first current detect circuit 728, the second currentdetect circuit 829, and the accessory dimmer connection AD via a signaldetector 1550, and processes the input as will be described in greaterdetail below. The signal detector 1550 is described in greater detail inU.S. Pat. No. 5,798,581, issued Aug. 25, 1998, entitled LOCATIONINDEPENDENT DIMMER SWITCH FOR USE IN MULTIPLE LOCATION SWITCH SYSTEM ANDSWITCH SYSTEM EMPLOYING SAME, the entire disclosure of which is herebyincorporated by reference.

FIG. 16A is a simplified block diagram of a four-way system 1500A, whichcomprises the multi-location dimmer 1502 and two three-way switches1503, 1504 coupled between an AC voltage source 1506 and a lighting load1508. In the four-way system 1500A, the multi-location dimmer 1502operates in the same manner as the smart four-way dimmer 802 of FIG. 8.Alternatively, the dimmer 1502 could be wired to the line side or theload side of a three-way system.

FIG. 16B is a simplified block diagram of a multi-location lightingcontrol system 1500B, which comprises the multi-location dimmer 1502coupled to an accessory dimmer 1505 via the accessory dimmer connectionAD. When operating in the multi-location system 1500B, themulti-location dimmer 1502 is responsive to an accessory control signalprovided by the accessory dimmer 1505 (as the dimmer 202 is responsiveto the accessory dimmer 204 in the prior art lighting control system 200of FIG. 2). Preferably, the accessory control signal is representativeof a command to either toggle, raise, or lower the intensity of thelighting load 1508. The signal detector 1550 is operable to provide anindication to the controller 1514 of whether the command is a toggle,raise, or lower command.

FIG. 17 is a state diagram 1560 summarizing the operation of themulti-location dimmer 1502. The dimmer 1502 begins in a default mode1562 when power to the dimmer is cycled (i.e., power is disconnected andthen immediately reconnected) or at power up as designated by “CP” inFIG. 17. In the default mode 1562, the dimmer 1502 operates as if thedimmer is installed in the four-way system 1500A (i.e., as the four-waydimmer 802 of FIG. 8). Accordingly, the controller 1514 of the dimmer1502 controls the triac 710 in response to the inputs provided by thefirst and second current sense circuits 728, 829.

If the dimmer 1502 receives an input on the accessory dimmer connectionAD (as designated by “AD” in FIG. 17), the dimmer 1502 changes to anaccessory dimmer mode 1564, in which the dimmer operates like the priorart dimmer 202 of FIG. 2. Accordingly, the dimmer 1502 is responsive toinputs provided at the accessory dimmer connection AD. The dimmer 1502is operable to return to the default mode 1562 when power is cycled tothe dimmer. If either of the three-way switches 1503, 1504 are coupledto the dimmer 1502, power will be disconnected and then immediatelyreconnected (i.e., cycled) each time either of the three-way switcheschange positions. Therefore, the dimmer 1502 changes back to the defaultmode 1562 from the accessory dimmer mode 1564 if a user changes theposition of either of the three-way switches 1503, 1504.

FIG. 18 is a rear perspective view of the multi-location dimmer 1502.The dimmer 1502 comprises an enclosure 1570, which houses the electricalcircuitry of the dimmer (i.e., the triac 710, the controller 1514, thecurrent sense circuits 728, 829, the signal detector 1550, etc.). Theenclosure 1570 is attached to a yoke 1572, which allows the dimmer 1502to be mounted to a standard electrical wallbox (not shown). The fourload terminals H1, H2, DH1, DH2 are arranged along the sides of theenclosure 1570. Preferably, the load terminals H1, H2, DH1, DH2 comprisescrew terminals, which may be tightened and loosened using a typicalscrewdriver to respectively connect and disconnect electrical wires toand from the electrical circuitry of the dimmer 1502. The dimmer 1502further comprises an accessory dimmer wire 1574 for coupling theaccessory connection AD to the accessory dimmer 1505.

Thus, dimmers 502, 602, 702, 802, and 1502 are configurable as three-wayor four-way (or multi-way) switches that improve upon prior art smartdimmers. In accordance with the present invention, the dimmers arerelatively inexpensive to manufacture, and are easier to install inexisting electrical systems than prior art smart dimmers providingthree-way and four-way switching functionality. For example, users arenot required to replace other existing three-way switches with accessorydimmers. Moreover, modifications to wiring of the other existingthree-way switches are avoided.

Furthermore, the various examples of three-way dimmers 502, 602, and 702illustrated herein are each shown as connected directly to the line-sideof the lighting control systems. One of ordinary skill in the art willrecognize that, in the alternative, the dimmers 502, 602, and 702 couldbe wired on the load-side of the systems.

Although the words “device” and “unit” have been used to describe theelements of the lighting control systems of the present invention, itshould be noted that each “device” and “unit” described herein need notbe fully contained in a single enclosure or structure. For example, thedimmer 502 of FIG. 5 may comprise a plurality of buttons in awall-mounted enclosure and a controller that is included in a separatelocation. Also, one “device” may be contained in another “device”. Forexample, the semiconductor switch (i.e., the controllably conductivedevice) is a part of the dimmer of the present invention.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art.Therefore, the present invention should not be limited by the specificdisclosure herein.

1. A dimmer switch for controlling the amount of power delivered from anAC power source to an electrical load, the dimmer switch adapted to becoupled either to a circuit including a single-pole double-throwthree-way switch or to a circuit including an accessory dimmer, thethree-way switch comprising a first fixed contact, a second fixedcontact, and a movable contact adapted to be coupled to either the powersource or the load the three-way switch having a first state in whichthe movable contact is contacting the first fixed contact and a secondstate in which the movable contact is contacting the second fixedcontact, the accessory dimmer comprising a terminal, the dimmer switchcomprising: a first load terminal adapted to be coupled to either thepower source or the load to which the three-way switch is not coupled; asecond load terminal adapted to be coupled to the first fixed contact ofthe three-way switch; a third load terminal adapted to be coupled to thesecond fixed contact of the three-way switch; an accessory dimmerconnection adapted to be coupled to the accessory terminal of theaccessory dimmer; a controllably conductive device electrically coupledto the first, second, and third load terminals, the controllablyconductive device having a conductive state in which the controllablyconductive device is controlled so as to be operable to deliver adesired amount of power to the load and a non-conductive state in whichthe controllably conductive device is controlled so as to be operable todeliver substantially no power to the load, the controllably conductivedevice arranged such that when the controllably conductive device is inthe conductive state and the dimmer switch is coupled to the circuit,the controllably conductive device is operable to allow a current to theload to flow between the first terminal and the second terminal orbetween the first terminal and the third terminal for at least a portionof each half-cycle of the AC power source; a sensing device electricallycoupled to at least one of the second load terminal and the third loadterminal, the sensing device operable to sense an electricalcharacteristic associated with the load terminal to which the sensingdevice is coupled; a controller operably coupled to the controllablyconductive device, the sensing device, and the accessory dimmerconnection, the controller operable to control the controllablyconductive device in response to either an output of the sensing devicein accordance with the electrical characteristic or a control signalprovided to the accessory dimmer connection; and a power supplyelectrically coupled in shunt electrical connection with thecontrollably conductive device and operable to provide power to thecontroller.
 2. The dimmer switch of claim 1, wherein the sensing devicecomprises a current sensing device.
 3. The dimmer switch of claim 2,wherein the current sensing device comprises a current transformer. 4.The dimmer switch of claim 3, wherein the current transformer comprisesa primary winding and a secondary winding, the primary winding of thecurrent transformer being coupled between the controllably conductivedevice and at least one of the second and third load terminals, and thesecondary winding of the current transformer being coupled so as toprovide the output of the sensing device to the controller.
 5. Thedimmer switch of claim 4, wherein the current sensing device is operableto detect whether a charging current is flowing in the power supply. 6.The dimmer switch of claim 5, wherein the sensing circuit is operable togenerate a control signal representative of whether the charging currentis flowing in the power supply and the controller is operable to changethe controllably conductive device between the conductive andnon-conductive states in response to the control signal.
 7. The dimmerswitch of claim 1, wherein the dimmer switch is operable to beginoperating in a default mode at power up, the controller operable tocontrol the controllably conductive device in response to the output ofthe sensing device in accordance with the electrical characteristic inthe default mode.
 8. The dimmer switch of claim 7, wherein the dimmerswitch is operable to begin operating in an accessory dimmer mode inresponse to receiving the control signal at the accessory dimmerconnection, the controller operable to control the controllablyconductive device in response to the control signal received via theaccessory dimmer connection in the accessory dimmer mode.
 9. The dimmerswitch of claim 8, further comprising: a signal detector coupled betweenthe controller and the accessory dimmer terminal, the signal detectoroperable to indicate to the controller whether the control signal isrepresentative of a command to toggle, raise, or lower the intensity ofthe electrical load.
 10. The dimmer switch of claim 1, wherein thecontrol signal is representative of a command to control the electricalload.
 11. The dimmer switch of claim 1, wherein the accessory dimmerconnection comprises an electrical wire extending from the dimmerswitch.
 12. The dimmer switch of claim 11, wherein the first, second,and third electrical load terminals comprises screw terminals.
 13. Thedimmer switch of claim 1, wherein the controllably conductive devicecomprises a bidirectional semiconductor switch.
 14. The dimmer switch ofclaim 1, wherein the controller comprises a microprocessor.
 15. Thedimmer switch of claim 1, further comprising: a fourth electrical loadterminal; and a second sensing device electrically coupled to at leastone of the first load terminal and the fourth load terminal, the secondsensing device operable to sense a second electrical characteristicassociated with the load terminal to which the second sensing device iscoupled; wherein the controller is coupled to the second sensing deviceand is operable to control the controllably conductive device inresponse to an output of the second sensing device in accordance withthe second electrical characteristic; and wherein the controllablyconductive device is arranged such that when the controllably conductivedevice is in the conductive state and the dimmer switch is coupled tothe circuit, current to the load flows between the first load terminaland one of the second load terminal and the third load terminal, orbetween the fourth load terminal and one of the second load terminal andthe third load terminal, depending on the output of the second sensingdevice.
 16. A dimmer switch for controlling the amount of powerdelivered from an AC power source to an electrical load, the dimmerswitch adapted to be coupled either to a circuit including first andsecond single-pole double-throw three-way switches or to a circuitincluding an accessory dimmer, the first three-way switch comprising afirst fixed contact, a second fixed contact, and a movable contactadapted to be coupled to the power source, the second three-way switchcomprising a first fixed contact, a second fixed contact, and a movablecontact adapted to be coupled to the load, the first and secondthree-way switches each having a first state in which the movablecontact is contacting the first fixed contact and a second state inwhich the movable contact is contacting the second fixed contact, theaccessory dimmer comprising an accessory terminal, the dimmer switchcomprising: a first load terminal adapted to be coupled to the firstfixed contact of the first three-way switch; a second load terminaladapted to be coupled to the second fixed contact of the first three-wayswitch; a third load terminal adapted to be coupled to the first fixedcontact of the second three-way switch; a fourth load terminal adaptedto be coupled to the second fixed contact of the second three-wayswitch; an accessory dimmer connection operable to receive a controlsignal from the accessory dimmer; a controllably conductive deviceelectrically coupled between the first load terminal and the third loadterminal for conducting a load current to the load, the controllablyconductive device having a conductive state in which the controllablyconductive device is controlled so as to be operable to deliver adesired amount of power to the load and a non-conductive state in whichthe controllably conductive device is controlled so as to be operable todeliver substantially no power to the load, the controllably conductivedevice arranged such that when the controllably conductive device is inthe conductive state and the dimmer switch is coupled to the circuit,the controllably conductive device is operable to allow a currentthrough the load flows from one of the first load terminal and thesecond load terminal to one of the third load terminal and the fourthload terminal for at least a portion of each half-cycle of the AC powersource; a first current sensing device electrically coupled between thefirst load terminal and the second load terminal and adapted to carrythe load current through the second load terminal, the first sensingdevice operable to generate a first control signal representative ofwhether a first current is flowing through the second load terminal; asecond current sensing device electrically coupled between the thirdload terminal and the fourth load terminal and adapted to carry the loadcurrent through the fourth load terminal, the second sensing deviceoperable to generate a second control signal representative of whether asecond current is flowing through the fourth load terminal; a signaldetector electrically coupled to the accessory dimmer connection andoperable to provide in response to the control signal an indication of acommand to control the electrical load; a controller operably coupled tothe controllably conductive device, the first and second current sensingdevices, and the signal detector, the controller operable to control thecontrollably conductive device either in response to the first andsecond control signals of the first and second current sensing devices,respectively, or the accessory control signal provided to the accessorydimmer connection; and a power supply coupled in shunt electricalconnection with the controllably conductive device and operable toprovide power to the controller.
 17. A method for controlling the amountof power delivered to an electrical load form an AC power source, themethod comprising the steps of: providing first, second, and thirdelectrical load terminals; providing an accessory connection;electrically coupling a controllably conductive device to the first,second, and third load terminals, the controllably conductive devicehaving a conductive state in which the controllably conductive device iscontrolled so as to deliver a desired amount of power to the load and anon-conductive state in which the controllably conductive device iscontrolled so as to deliver substantially no power to the load; sensingan electrical characteristic associated with at least one of the secondload terminal and the third load terminal; controlling the controllablyconductive device in accordance with the sensed electricalcharacteristic, such that a current through the load flows between thefirst load terminal and the second load terminal, or between the firstload terminal and the third load terminal; receiving a control signalvia the accessory terminal connection; and controlling the controllablyconductive device in accordance with the received control signal.